Modern rock drilling rigs comprise one or more hydraulic pumps, the pressure fluid flow obtained from which is guided by means of suitable valves along pressure fluid channels to hydraulic actuators, such as the percussion device, the rotation device and the feed device of the rock drill machine, comprised by the rock drilling rig, and further to the cylinders that move the booms and to the turning device of the carrier. The hydraulic pressure and hydraulic flow obtained from the hydraulic pump are adjusted with adjusting members arranged in the pressure fluid channels of the actuators, such as with pressure regulators and restrictors in a manner enabling the feed of necessary hydraulic power to each actuator. Unfortunately, such adjusting members cause significant power losses in a hydraulic system. A further drawback in present systems is that when an actuator receiving a large oil flow is used, e.g. a boom cylinder, it may affect the pressure and flow of the entire hydraulic system and thus interfere with the operation of other actuators connected to the hydraulic system.